Its been a hefty few years since i last played this game, I honestly just found an old drawing i did of the Sylvorpas (Which apparently at the time I had an obsession with lol) and thought to take a gander.
Im not sure where to start picking up again, coming back to it after so long is a bit confusing. Any tips/advice on what i should work on first?

depends on where you are, really? How far are you progression-wise? What's your team?
Is there anything you feel like you need to know?

If you want to give the high level combat stuff a go, then you will want to do a check of your team to see if they're up to the standard for the lost grove.

But it's not necessary to focus on combat. Other things I can think of as focuses are doing a review of stables to see if there are things you'd want to release to make room for new pets. Breeding projects are the main thing I focus on, and those work on a scale of many months, but breeding some individual cool pets by finding nice matches for your favourites is also fun.

Lots of people like to collect themed pets, which are mostly available from festivals, so not at the moment. But there are often some givaways or sales with them, or for aquiring cool pets generally.

Oh, and it's pretty much always a good idea to send pets on missions at the cities on the map. It gives good amounts of gold.